Infection and Immunity
Infection and Immunity
Eastem europ Western& Central Asia North Europe America 1 million 59?0 East asia Pac 4Q000 No anbbean South 1 million middle 420000East south east asia 6.1 million subsaharan Latin africa America australia 28.1 new Zealand million million 15000 Total H/V-Infected Population (December 2001): 40 million
What does a pathogen have to do? Infect (infest) a host Reproduce(replicate) itself Ensure that its progeny are transmitted to another host
What does a pathogen have to do? • Infect (infest) a host • Reproduce (replicate) itself • Ensure that its progeny are transmitted to another host
Mechanisms of Transmission Aerosols-inhalation of droplets, e.g Rhinoviruses the 'Common Cold Virus or Adenoviruses Faecal-Oral -e.g. Astroviruses, Caliciviruses these viruses cause acute gastroenteritis Vector-borne -e.g. in Arthropods such as mosquitos, ticks, fleas: Arboviruses Close personal contact -especially exchange of bodily fluids: Sex; Blood, e.g. Herpesviruses
Mechanisms of Transmission • Aerosols - inhalation of droplets, e.g. Rhinoviruses, the 'Common Cold Virus' or Adenoviruses. • Faecal-Oral - e.g. Astroviruses, Caliciviruses; these viruses cause acute gastroenteritis. • Vector-borne - e.g. in Arthropods such as mosquitos, ticks, fleas: Arboviruses. • Close personal contact - especially exchange of bodily fluids: Sex; Blood, e.g. Herpesviruses
Entry into the Host Skin-dead cells, therefore cannot support virus replication. Most viruses which infect via the skin require a breach in the physical integrity of this effective barrier, e. g cuts or abrasions. Many viruses employ vectors, e.g. ticks mosquitos or vampire bats to breach the barrier. Respiratory tract- In contrast to skin, the respiratory tract and all other mucosal surfaces possess sophisticated immune defence mechanisms, as well as non-specific inhibitory mechanisms [ciliated epithelium, mucus secretion, lower temperature] which viruses must oVerCOme
Entry into the Host • Skin- dead cells, therefore cannot support virus replication. Most viruses which infect via the skin require a breach in the physical integrity of this effective barrier, e.g. cuts or abrasions. Many viruses employ vectors, e.g. ticks, mosquitos or vampire bats to breach the barrier. • Respiratory tract- In contrast to skin, the respiratory tract and all other mucosal surfaces possess sophisticated immune defence mechanisms, as well as non-specific inhibitory mechanisms (cilliated epithelium, mucus secretion, lower temperature) which viruses must overcome. •
Entry into the Host Gastrointestinal tract-ahostile environment; gastric acid, bile salts, etc Genitourinary tract-relatively less hostile than the above, but less frequently exposed to extraneous viruses Conjunctiva-an exposed site and relatively unprotected
Entry into the Host • Gastrointestinal tract- a hostile environment; gastric acid, bile salts, etc • Genitourinary tract-relatively less hostile than the above, but less frequently exposed to extraneous viruses (?) • Conjunctiva - an exposed site and relatively unprotected
Sites of virus entry Eyes(conjunctiva Mouth Respiratory tract Skim: abrasion arthropod vectors Alimentary canal Urogenital tract
Sites of virus entry
Transmission patterns HorzontalTransmission: Direct person-to person spread Verticaltransmission: Relies on PerSiSTe cE of the agent to transfer infection from parents to offspring. Several forms of vertical transmission can be distinguished: 1 Neonatalinfection at birth, e.g. gonorrhoea AIDS 2. Infection in utero e.g. syphilis, CMV, Rubella CCRSLAIDS 3. Germ line infection -via ovum or sperm
Transmission patterns • Horizontal Transmission: Direct person-toperson spread. • Vertical Transmission:Relies on PERSISTENCE of the agent to transfer infection from parents to offspring. Several forms of vertical transmission can be distinguished: • 1.Neonatal infection at birth, e.g. gonorrhorea, AIDS. • 2.Infection in utero e.g. syphilis, CMV, Rubella (CRS), AIDS. • 3. Germ line infection - via ovum or sperm
Primary Replication Having gained entry to a potential host, the virus must initiate an infection by entering a susceptible cell. This frequently determines whether the infection will remain localized at the site of entry or spread to become a systemic infection
Primary Replication • Having gained entry to a potential host, the virus must initiate an infection by entering a susceptible cell. This frequently determines whether the infection will remain localized at the site of entry or spread to become a systemic infection
Localized infections iruses PrimaryReplication Rhinoviruses URT Rotaviruses Intestinal epithelium Papillomaviruses Epidermis
Localized Infections • Viruses Primary Replication • Rhinoviruses U.R.T. • Rotaviruses Intestinal epithelium • Papillomaviruses Epidermis
